The present invention relates generally to expansion joints, and more particularly, to a purged expansion joint with a floating liner seal.
In general, piping systems must be designed so that they will not fail because of excessive stresses, or leak at joints because of expansion or deflection of the pipe elements. In many instances these requirements can be attended to by use of a so-called expansion joint. In such a joint, a length of tubing or pipe to be joined typically has a reduced diameter end portion which is received by another tube or pipe. The reduced diameter end portion is sometimes referred to as a liner and is dimensioned relative to the receiving pipe so as to allow axial and lateral movement of the pipe elements relative to one another. A coaxial bellows unit is then used to connect and seal the two pipe elements by forming a flexible external shroud over the junction of the pipes. The bellows, liner and pipe elements together define an expansion joint cavity or annular region around the junction of the pipes. The liner guides movement of the joint and also protects the flexible bellows from direct contact with the fluid being handled.
Since expansion joints must absorb a variety of movements simultaneously, including axial deflection (i.e. parallel to the axis of the pipe or duct), lateral deflection (i.e. perpendicular to the axis of the pipe or duct), and angular deflection (i.e. rotation about an axis perpendicular to the axis of the pipe or duct), it is not feasible for the liner to fit tightly within the receiving pipe. Therefore, a certain amount of service fluid or particulates from the flowstream will generally reach the bellows unit by traveling through the gap between the liner and the inner surface of the receiving pipe. Depending on the nature of the fluid materials being transported and the particular bellows material employed, such influx may result in damage to the bellows or impairment of the elasticity of the joint. In applications where a stagnancy in the flowstream can cause an unwanted chemical reaction, for example in methylacrylate plants, the introduction of particulate from the flowstream into the expansion joint is particularly unacceptable.
In order to avoid the problems associated with communication of particulates or service fluid into an expansion joint, there have been developed purged systems which circulate a purge fluid into the expansion joint cavity. For example, U.S. Pat. No. 4,576,404 to Weber describes a vertically-oriented bellows expansion joint which incorporates an internal flange and cylindrical weir to define an inner flushing reservoir adjacent to the expansion bellows.
Purged expansion joints have heretofore been limited to use under certain conditions and have required large flow rates to prevent the intrusion of particulates or service fluid from the flowstream into the expansion joint cavity. However, the maintenance of large flow rates in a purged expansion joint decreases operating efficiency and is likely to introduce impurities into the flowstream. Moreover, since suitable purge fluids are usually costly to produce and to transport in a system, purged expansion joints have been costly to operate. In fact, the purge fluid is often considered more valuable than the typical flowstream.